Circuit card rack system and method

ABSTRACT

A method of maintaining a circuit card in a card rack and a circuit card rack system are disclosed. A card rack including a laterally oriented clamping slot is provided. The clamping slot is at least partially formed from a temperature-contractible material. A circuit card having a clamped side region is provided. At least a portion of the clamped side region is inserted into the clamping slot. A predetermined temperature differential is applied to the clamping slot to reduce a longitudinal dimension of at least a portion of the clamping slot. A compressive force is exerted on the portion of the clamped side region which is located longitudinally within the clamping slot, via thermal expansion of the clamping slot.

RELATED APPLICATIONS

This application claims priority from U.S. patent application Ser. No.14/943,385, filed 17 Nov. 2015, which is incorporated herein in itsentirety.

TECHNICAL FIELD

This disclosure relates to an apparatus and method for use of a circuitcard rack system and, more particularly, to a circuit card rack systemand a method of maintaining a circuit card in a circuit rack.

BACKGROUND

It may be desirable to install modules (e.g., chip-carrying circuitcards, printed wiring boards, or the like) in a card rack for acryogenic application, such as a superconducting supercomputer. In thisuse application, it may be desirable both to accommodate large modulesand to provide uniform clamping force between the cards and the rack.The card rack should maintain clamping force at cryogenic temperatures(e.g., less than or equal to about 123K), and low thermal resistancebetween the rack and the card(s) carried thereby is required. Desiredthermal performance can be achieved by uniform contact pressure betweenthe cards and the card rack.

The current state of the art approach to module/card rack installationincludes the use of wedgelocks. These have been used in currently knownassemblies. The limitation of the wedgelock approach is that both thecard rack and module/card must of the same material in order to achievedesired thermal conductivity in the use environment. In addition, thewedgelock system requires multiple very small shims or wedges, addingcomplexity to assembly of the system. Wedgelocks are also extremelyexpensive, with multiple wedgelocks needed for a particular instance ofa card rack system. There is also a risk of adverse effects to thesystem if a wedgelock malfunctions (e.g., does not clamp as intended) oris located out of position (e.g., falls loose and interferes withelectrical connections in the system). Finally, because wedgelocks arepresent at discrete sites along the card slots, there are local high/lowclamping force areas along the length of the card slot, as well asrelatively low thermal transfer between the modules and the card rackbecause of the noncontiguous placement of the wedgelocks along the cardslot.

SUMMARY

In an embodiment, a method of maintaining a circuit card in a card rackis disclosed. A card rack including a laterally oriented clamping slotis provided. The clamping slot is at least partially formed from atemperature-contractible material. A circuit card having a clamped sideregion is provided. At least a portion of the clamped side region isinserted into the clamping slot. A predetermined temperaturedifferential is applied to the clamping slot to reduce a longitudinaldimension of at least a portion of the clamping slot. A compressiveforce is exerted on the portion of the clamped side region which islocated longitudinally within the clamping slot, via thermal expansionof the clamping slot.

In an embodiment, a circuit card rack system is provided. A card rackincludes a laterally oriented clamping slot. The clamping slot is atleast partially formed from a temperature-contractible material. Acircuit card has a clamped side region. The circuit card has anoperative configuration with at least a portion of the clamped sideregion being inserted into the clamping slot. When the circuit card isin the operative configuration, applying a predetermined temperaturedifferential to the clamping slot reduces a longitudinal dimension of atleast a portion of the clamping slot via thermal expansion of theclamping slot, thus causing exertion of a compressive force on theportion of the clamped side region which is located longitudinallywithin the clamping slot.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding, reference may be made to the accompanyingdrawings, in which:

FIG. 1A is a schematic partial side view of one aspect of the invention;

FIG. 1B is a schematic partial top view of the aspect of FIG. 1A;

FIG. 2A is a schematic side view of the aspect of FIG. 1A;

FIG. 2B is a schematic top view of the aspect of FIG. 2A;

FIG. 3A is a schematic side view of the aspect of FIG. 1A with a firstcomponent option;

FIG. 3B is a perspective top view of FIG. 3A;

FIG. 4A is a schematic side view of the aspect of FIG. 1A with a secondcomponent option;

FIG. 4B is a perspective top view of FIG. 4A;

FIG. 5A is a schematic side view of the aspect of FIG. 1A with a thirdcomponent option;

FIG. 5B is a perspective top view of FIG. 5A;

FIG. 6A is a schematic side view of the aspect of FIG. 1A with a fourthcomponent option;

FIG. 6B is a perspective top view of FIG. 6A;

FIG. 7 is a perspective side view of the aspect of FIG. 6A;

FIGS. 8-11 depict a sequence of operation of any configuration of theaspect of FIG. 1A; and

FIG. 12 is a flowchart illustrating a method of operation of anyconfiguration of the aspect of FIG. 1A.

DESCRIPTION OF ASPECTS OF THE DISCLOSURE

This technology comprises, consists of, or consists essentially of thefollowing features, in any combination.

Though certain of the Figures may include gaps between components, itshould be understood that the Figures are schematic, and that these gapsare included for ease of depiction. There may or may not actually be agap between these components in actuality, and one of ordinary skill inthe art can readily determine (optionally with reference to the text anddrawings of this application) the presence or absence of gaps in aparticular use environment for a particular operational condition of thedepicted components, without regard to the presence or absence of gapsin the Figures.

It will be understood that when an element is referred to as being “on,”“attached” to, “connected” to, “coupled” with, “contacting,” etc.,another element, it can be directly on, attached to, connected to,coupled with or contacting the other element or intervening elements mayalso be present. In contrast, when an element is referred to as being,for example, “directly on,” “directly attached” to, “directly connected”to, “directly coupled” with or “directly contacting” another element,there are no intervening elements present. It will also be appreciatedby those of skill in the art that references to a structure or featurethat is disposed “directly adjacent” another feature may have portionsthat overlap or underlie the adjacent feature, whereas a structure orfeature that is disposed “adjacent” another feature may not haveportions that overlap or underlie the adjacent feature.

Spatially relative terms, such as “under,” “below,” “lower,” “over,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms can encompass different orientations of adevice in use or operation, in addition to the orientation depicted inthe figures. For example, if a device in the figures is inverted,elements described as “under” or “beneath” other elements or featureswould then be oriented “over” the other elements or features.

It will be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. Thus, a “first” element discussed below couldalso be termed a “second” element without departing from the teachingsof the present disclosure. The sequence of operations (or steps) is notlimited to the order presented in the claims or figures unlessspecifically indicated otherwise.

FIGS. 1A-1B depict a circuit card rack system 100. A card rack 102includes a laterally oriented clamping slot 104. The lateral directionis indicated at L_(A), and is in the left-right direction, in theorientation of FIG. 1A, and is within the plane of the page, in theorientation of FIG. 1B. The longitudinal direction (L_(O)) issubstantially perpendicular to the lateral direction—in the top-bottomdirection, in the orientation of FIG. 1A. The clamping slot 104 is atleast partially formed from a temperature-contractible material.

A circuit card 106 has a clamped side region 108. It is contemplatedthat the circuit card 106 assembly shown schematically in the Figuresmay include a heat sink or other structure—the term “circuit card” isused herein to generally reference a card or substrate upon which one ormore circuits are or can be located, along with any desired additionalstructures which would be recognized by one of ordinary skill in the artas associated with that card or substrate itself.

The circuit card 106 has an operative configuration with at least aportion of the clamped side region 108 being inserted into the clampingslot 104, such as the one-sided or cantilevered installation shown inFIGS. 1A-1B. The circuit card 106 may have a substantially planarcircuit card body 110 including at least one laterally oriented sideedge 112 and circuit card top and bottom surfaces, 114 and 116,respectively, longitudinally separated by the circuit card body 110.Optionally, all or part of the perimeter of the circuit card body 110(as shown in FIG. 1B as a substantially rectilinear footprint in thelateral plane) may be a “side edge” 112, and one of ordinary skill inthe art will understand what portions of a particular circuit card 106are performing a “side edge” 112 function.

At least a portion of the side edge 112 is included in the clamped sideregion 108. In addition, for most use environments of the circuit cardrack system 100, at least a portion of the circuit card top and bottomsurfaces, 114 and 116 will also be included in the clamped side region.As a general principle, the clamped side region 108 will be a portion ofthe circuit card 106 which is located within the recess of the clampingslot 108, and optionally bears a direct relationship to the lateraldepth of the clamping slot 108. One of ordinary skill in the art will beable to determine the bounds of a “clamped side region” 108 for aparticular use environment of the circuit card rack system 100.

FIGS. 2A-2B are similar to FIGS. 1A-1B, except that, instead of thecantilevered configuration of FIGS. 1A-1B, the circuit cards 106 aresupported on both sides by card racks 102. While the card racks 102 areshown schematically as being different structures in FIGS. 2A-2B, it isalso contemplated that the card racks 102 could be part of a singlestructure. As with FIGS. 1A-1B, the circuit card rack system 100 ofFIGS. 2A-2B is depicted as having a plurality of clamping slots 104,each of which is associated with a separate circuit card 106; however,it is contemplated that any number of clamping slots 104 and/or circuitcards 106 could be provided to a single circuit card rack system 100,and that there need not be a direct correspondence between the number ofclamping slots 104 and the number of circuit cards 106 for a particularcircuit card rack system 100.

With further reference to particularly FIG. 2A, the card rack 102 mayinclude first and second laterally oriented, laterally spaced,longitudinally aligned clamping slots, 104′ and 104″, respectively, asshown in this Figure. (The “prime” and “double prime” marks are usedherein to indicate portions of specific ones of numbered elements whichare generally indicated, as a type, by an element number without such asuperscript marking.)

Each of the first and second clamping slots 104′ and 104″ is disposed toone lateral side of an open card volume 118 of the card rack 102. Whenpresent, the first and second clamping slots 104′ and 104″ may each beat least partially formed from a temperature-contractible material. Inthis example, the circuit card 106 is a substantially planar circuitcard 106′ having first and second laterally spaced clamped side regions108′ and 108″, respectively. The circuit card 106′ shown in FIGS. 2A-2Bhas an operative configuration with at least a portion of the firstclamped side region 108′ being inserted into the first clamping slot104′ and at least a portion of the second clamped side region 108″ beinginserted into the second clamping slot 104″. In this example, thecircuit card 106′ laterally spans at least a portion of the open cardvolume 118 of the card rack 102.

As will be discussed further below, and with reference to any circuitcard rack system 100 (regardless of the Figure in which it is shownherein), when the circuit card 106 is in the operative configuration(i.e., with a desired amount of the clamped side region 108 beinginserted into a corresponding clamping slot 104), applying apredetermined temperature differential to the clamping slot 104 reducesa longitudinal dimension of at least a portion of the clamping slot 104via thermal expansion of the clamping slot 104, because the clampingslot 104 is at least partially formed from a temperature-contractiblematerial. This dimensional reduction of the clamping slot 104 causesexertion of a compressive force on the portion of the clamped sideregion 108 which is located longitudinally within the clamping slot 104.For most use environments, the compressive force will be substantiallylongitudinally oriented. However, it is also contemplated that alaterally oriented compressive force could also or instead be exertedupon the clamped side region 108, such as by lateral dimensionalreduction of the “blind end” (toward the left, in the orientation ofFIG. 1A) and/or of at least one end face (when present) of the clampingslot 104, as desired.

The predetermined temperature differential may be a positive (heating)or a negative (cooling) temperature differential, as desired. Forexample, in a cryogenic use environment, the temperature differentialwill be negative. Likewise, the thermal expansion of the clamping slot104 may be negative thermal expansion (i.e., contraction). Thepredetermined temperature differential may be provided in any desiredmanner such as, but not limited to, cooling/heating channels in the cardrack 102, exposure of the entire circuit card rack system 100 to adesired heating/cooling energy, thermal siphon, cryogenic liquids,dilution refrigeration, Gifford-McMahon (GM) or pulse tube cryocoolers,local exposure of at least a portion of the clamping slot 104 to aheating/cooling agent (e.g., liquid nitrogen), or any combination ofthese or other temperature differential generating mechanism.

One of ordinary skill in the art will be able to configure at least oneof the temperature-contractible material, any dimension of the clampingslot 104, any dimension of the clamped side region 108, and thetemperature differential to achieve a predetermined compressive forcebetween the clamping slot 104 and the clamped side region 108, asdesired.

As an example, at least the clamping slot 104 portion of the card rack102 and at least the clamped side region 108 of the circuit card 106 maybe made from different materials, having different coefficients ofthermal expansion (“CTE”). For example, the circuit card 106 could bemade from steel and the card rack 102 from aluminum. At roomtemperature, the clamped side region 108 would slide in and out of theclamping slot 104 with a tight sliding fit (e.g., a gap therebetween ofapproximately 0.010″). It should be understood, though, that the gapbetween the clamped side region 108 and the clamping slot 104 could beadjusted for desired relative sliding functions (e.g., to make thecircuit card 106 harder or easier to slide relative to the card rack102) by the use of different materials.

As the circuit card rack system 100 is cooled to cryogenic temperatures,the card rack 102 reduces its size at a faster rate than does thecircuit card 106, due to the difference in CTEs. The circuit card racksystem 100 is “self-tightening”, so does not need to be pre-tightened(thus resulting in greater thermal stresses over the cooling/heatingcycle), as would a wedgelock system.

It is even contemplated that the clamped side region 108 may remainrelatively constant-dimension, in some use applications for the circuitcard rack system 100. In general, the geometry of the clamping slot 104will reduce proportionally to its initial length. This means that thelongitudinal dimension of the clamping slot 104 will be reduced by alarger total amount because the longitudinal dimension is much largerthan the lateral dimension of the clamping slot 104.

Until clamping begins, no compressive force generated by the thermalmismatch stress will be applied to the circuit card 106. Clamping of thecircuit card 106 will begin a predicted temperature that is determinedby the CTEs of the materials of the clamping slot 104 and the clampedside region 108, and by the initial gap conditions between these twostructures. When desired clamping force is present, the thermalperformance will be realized and the remaining thermal stress-inducedclamping force will be applied to the clamped side region 108. Theclamping force (i.e., thermally-induced compressive force which acts tomaintain the clamped side region 108 in the clamping slot 104) is atleast partially determined by the material CTEs, initial gap, and thematerial moduli of elasticity (Young's Modulus).

Stated differently, the temperature-contractible material of the cardrack 102 may be a first temperature-contractible material having a firstcoefficient of thermal expansion and the temperature differential is afirst temperature differential. The circuit card 106, then, may be atleast partially formed from a second temperature-contractible materialdifferent from the first temperature-contractible material and having asecond coefficient of thermal expansion which is different from thefirst coefficient of thermal expansion. When the circuit card is in theoperative configuration as shown in FIGS. 1A-2B, a selected one of thefirst temperature differential and a predetermined second temperaturedifferential may be applied to the clamped side region 108 to reduce alongitudinal dimension of at least a portion of the clamped side region108 via thermal expansion (which could be negative thermal expansion) ofthe clamped side region 108. The thermally-induced reduction of thelongitudinal dimension of the clamped side region 108 is less than thethermally-induced reduction of the longitudinal dimension of acorresponding portion of the clamping slot 104. In this manner, thethermal expansion mismatch between the clamping slot 104 and the clampedside region 108 causes exertion of sufficient compressive force on theportion of the clamped side region 108 within the clamping slot 104 tomaintain the circuit card 106 in the card rack 102.

With reference now to FIGS. 3A-7, various options for the circuit cardrack system 100 are shown. In FIGS. 3A-4B, the circuit card 106 includesan edge feature 320 extending substantially along at least a portion ofthe side edge 112. For example, the edge feature 320 could be a“wedgelock replacement” adaptation allowing previously used circuitcards 106 to be adapted for use with a circuit card rack system 100. Theedge feature 320 has a longitudinal thickness that is substantiallygreater than a laterally adjacent portion of the circuit card 106. Thatis, the edge feature 320 is substantially locally thicker than a portionof the circuit card 104 located laterally inward from the edge feature320—though squared-off edge features 320 is shown, it is alsocontemplated that the edge feature 320 may have a more gradualtransition to a remaining circuit card top and/or bottom surfaces 114and 116. (Again, it should be noted that the “circuit card top and/orbottom surfaces 114 and 116” could include a heat sink to which a cardsubstrate is mounted/laminated, or any other associated structuresmaking up a general “circuit card” element.) As shown in FIGS. 3A-4B,the edge feature 320 may be at least partially inserted into theclamping slot 104 in the operative configuration.

The difference between the arrangements shown in FIGS. 3A-3B and 4A-4Bis that, in the former, the edge feature 320 is partially on the circuitcard top surface 114 and partially on the circuit card bottom surface116, thus “suspending” the majority of the circuit card 106longitudinally between the top and bottom faces of the clamping slot104—i.e., “in-plane”. In contrast, in the latter Figures, the edgefeature 320 is wholly on a chosen one of the circuit card top and bottomsurfaces 114 and 116, thus “pinning” the other of the circuit card topand bottom surfaces 114 and 116 against a respective top or bottom faceof the clamping slot 104. FIGS. 4A-4B show the edge feature 320 as beingon the circuit card top surface 114, but the edge feature 320 couldinstead be on the circuit card bottom surface 116—basically, invertingthe views of FIGS. 4A-4B.

Turning now to FIGS. 5A-7, at least one spacer 522 could be interposedbetween at least a portion of the clamped side region 108 and at least aportion of the clamping slot 104. For example, as shown in FIGS. 5B and6B, a plurality of relatively small spacers 522 could be lined up alongthe clamped side region 108, which would allow for flexibility in thelength of the interface between the spacers 522 and the clamped sideregion 108. Optionally, and as shown, a rack aperture 524 could beprovided to the card rack(s) 102, to facilitate access to the spacers522 from a side of the card rack 102 opposite the clamping slot 104.

FIGS. 5A-5B and 6A-6B show, respectively, two different configurationsof edge features 320 with spacers 522. However, it is also contemplatedthat one or more spacers 522 could be provided to a circuit card 106without an edge feature 320.

As depicted in FIG. 7, the spacers 522, when present, may be L-shaped(or any other shape, as desired) “shim” type structures which can beused to at least partially occupy a portion of the clamping slot 104which is not occupied by the clamped side region 108. For example, andas shown, the spacers 522 may be used to “snug up” the circuit card 106by pressing the clamped side region 108 longitudinally against one faceof the clamping slot 104. This may allow for different dimensionaltolerances between the structures of the circuit card rack system 100,even facilitate the use of different thickness, or differentlyconfigured, circuit cards 106 with a single card rack 102 configuration.

The spacers 522, when present, may be made of the same material as oneor both of the clamping slot 104 and the clamped side region 108, or maybe made of a different material than either. For example, the spacers522 may be made from Delrin® acetal homopolymer resin, available fromDupont USA of Wilmington, Del. The spacers 522 may have a different CTEthan at least the portion of the clamping slot 104 directly adjacent tothe spacers 522. For example, Delrin® spacers have a larger CTE thanmost metals, which will facilitate allowing a larger gap between theclamping slot 104 and the clamped side region 108 at room temperature,thus facilitating slide-in of the circuit card 106 into the card rack102.

FIGS. 8-11 illustrate an example sequence of use of the circuit cardrack system 100. In FIG. 8, the circuit card 106 is placed (e.g., slid)into the card rack to position the clamped side region 108 into theclamping slot 104. As shown in FIG. 9, a gap “G” between the clampedside region 108 and the clamping slot 104 exists, which allows for thecircuit card 106 to be adjusted into a desired operative configuration.

In FIG. 10, a predetermined temperature differential “T” is applied toat least a portion of the clamping slot 104 in any suitable manner, andoptionally also to at least a portion of the clamped side region 108.The predetermined temperature differential reduces a longitudinaldimension of at least a portion of the clamping slot 104, thus causingexertion of a compressive force “F” on the portion of the clamped sideregion 108 which is located longitudinally within the clamping slot 104,via thermal expansion (which, again, could be negative thermalexpansion) of the clamping slot 104, as shown in FIG. 11. For most useenvironments of the circuit card rack system 100, there will besufficient compressive force exerted on the portion of the clamped sideregion 108 to maintain the circuit card 106 in the card rack 102.

As long as the circuit card 106 is desired to be maintained under thecompressive force F, the predetermined temperature differential T couldbe maintained at a steady-state temperature chosen (optionally inconjunction with specific dimensions and materials of the circuit cardrack system 100) to maintain the compressive force F. When the clampingslot 104 is exerting a compressive force F on the portion of the clampedside region 108 which is located longitudinally within the clamping slot104, this compressive force F can be reduced by applying a predeterminedtemperature differential to the clamping slot 104 to increase alongitudinal dimension of at least a portion of the clamping slot 104and thereby reduce the compressive force being exerted—i.e., theclamping process is reversed. Once the compressive force F has beensufficiently reduced, the circuit card 106 may be removed from the cardrack 102

FIG. 12 is a flowchart depicting at least a portion of an examplesequence of operation of the circuit card rack system 100. In firstaction block 1226, a card rack 102 including a laterally orientedclamping slot 104 is provided. In second action block 1228, a circuitcard 106 having a clamped side region 108 is provided. In third actionblock 1230, at least a portion of the clamped side region 108 of thecircuit card 106 is inserted into the clamping slot 104 of the card rack102. In fourth action block 1232, a predetermined temperaturedifferential is applied to the clamping slot 104 to reduce alongitudinal dimension of at least a portion of the clamping slot 104. Acompressive force F is then exerted on the portion of the clamped sideregion 108 which is located longitudinally within the clamping slot 104,via thermal expansion of the clamping slot 104.

The above description presumes that the clamped side region 108 and theclamping slot 104 are each comprised of a homogenoustemperature-contractible material. However, it is contemplated that theclamped side region 108 and/or the clamping slot 104 could additionallyor alternatively be comprised of a combination of materials (e.g., astack of different materials, a laminate, an alloy, a composite, or anyother multi-material combinations), and thus the relative CTEs can be“tuned” for particular clamping results.

In addition to the compressive force developed between the clamped sideregion 108 and the clamping slot 104, this connection can also assistwith providing a large-surface-area interface to assist with thermalenergy transfer between the circuit card 106 and the card rack 102. Fora conventional wedgelock, the material that is being pressed into thecard rack provides the primary thermal interface. The direction throughthe wedgelock is an inferior thermal path because it includes additionalsurface resistances and it has a reduced cross section (wedgelocks havehollow parts to allow articulation). This problem is reduced by theconstant and relatively large surface contact between the clamped sideregion 108 and the clamping slot 104. In contrast, a supermajority of asurface area of the clamping slot 104 of the circuit card rack system100 is in thermal contact with a supermajority of a surface area of theclamped side region 108 to achieve a predetermined rate of thermalenergy transfer therebetween, this predetermined rate of thermal energytransfer being significantly higher than a similar rate achievablethrough a thermal path using known wedgelock clamping systems.

While aspects of this disclosure have been particularly shown anddescribed with reference to the example embodiments above, it will beunderstood by those of ordinary skill in the art that various additionalembodiments may be contemplated. For example, the specific methodsdescribed above for using the apparatus are merely illustrative; one ofordinary skill in the art could readily determine any number of tools,sequences of steps, or other means/options for placing theabove-described apparatus, or components thereof, into positionssubstantively similar to those shown and described herein. Any of thedescribed structures and components could be integrally formed as asingle unitary or monolithic piece or made up of separatesub-components, with either of these formations involving any suitablestock or bespoke components and/or any suitable material or combinationsof materials. Any of the described structures and components could bedisposable or reusable as desired for a particular use environment. Anycomponent could be provided with a user-perceptible marking to indicatea material, configuration, at least one dimension, or the likepertaining to that component, the user-perceptible marking aiding a userin selecting one component from an array of similar components for aparticular use environment. A “predetermined” status may be determinedat any time before the structures being manipulated actually reach thatstatus, the “predetermination” being made as late as immediately beforethe structure achieves the predetermined status. Though certaincomponents described herein are shown as having specific geometricshapes, all structures of this disclosure may have any suitable shapes,sizes, configurations, relative relationships, cross-sectional areas, orany other physical characteristics as desirable for a particularapplication. Any structures or features described with reference to oneembodiment or configuration could be provided, singly or in combinationwith other structures or features, to any other embodiment orconfiguration, as it would be impractical to describe each of theembodiments and configurations discussed herein as having all of theoptions discussed with respect to all of the other embodiments andconfigurations. A device or method incorporating any of these featuresshould be understood to fall under the scope of this disclosure asdetermined based upon the claims below and any equivalents thereof.

Other aspects, objects, and advantages can be obtained from a study ofthe drawings, the disclosure, and the appended claims.

We claim:
 1. A circuit card rack system, comprising: a card rackincluding a laterally oriented clamping slot, the clamping slot being atleast partially formed from a temperature-contractible material, thetemperature-contractible material being a first temperature-contractiblematerial having a first coefficient of thermal expansion; and a circuitcard having a clamped side region and being at least partially formedfrom a second temperature-contractible material different from the firsttemperature-contractible material and having a second coefficient ofthermal expansion which is different from the first coefficient ofthermal expansion, the circuit card having an operative configurationwith at least a portion of the clamped side region being inserted intothe clamping slot; wherein, when the circuit card is in the operativeconfiguration, applying a predetermined temperature differential to theclamping slot reduces a longitudinal dimension of at least a portion ofthe clamping slot via thermal expansion of the clamping slot, andapplying the predetermined temperature differential to the clamped sideregion reduces the longitudinal dimension of at least a portion of theclamped side region which is located longitudinally within the clampingslot, the thermally-induced reduction of the longitudinal dimension ofthe clamped side region being less than the thermally-induced reductionof the longitudinal dimension of the claiming slot, thus causingexertion of a compressive force on the portion of the clamped sideregion which is located longitudinally within the clamping slot viathermal expansion of the clamping slot.
 2. The system of claim 1,wherein the predetermined temperature differential is a negativetemperature differential, and the thermal expansion of the clamping slotis negative thermal expansion.
 3. The system of claim 1, wherein thecard rack includes first and second laterally oriented, laterallyspaced, longitudinally aligned clamping slots, each disposed to onelateral side of an open card volume of the card rack, the first andsecond clamping slots each being at least partially formed from thefirst temperature-contractible material; the circuit card is asubstantially planar circuit card having first and second laterallyspaced clamped side regions; and the circuit card has an operativeconfiguration with at least a portion of the first clamped side regionbeing inserted into the first clamping slot and at least a portion ofthe second clamped side region being inserted into the second clampingslot with the circuit card laterally spanning at least a portion of theopen card volume of the card rack.
 4. The system of claim 1, wherein thecircuit card has a substantially planar circuit card body including atleast one laterally oriented side edge and circuit card top and bottomsurfaces longitudinally separated by the circuit card body, the circuitcard includes an edge feature extending substantially along at least aportion of the side edge, the edge feature has a longitudinal thicknessthat is substantially greater than a laterally adjacent portion of thecircuit card, and the edge feature is at least partially inserted intothe clamping slot in the operative configuration; and wherein the edgefeature is located a selective one of: wholly on a chosen one of thecircuit card top and bottom surfaces, and partially on the circuit cardtop surface and partially on the circuit card bottom surface.
 5. Thesystem of claim 1, including a spacer interposed between at least aportion of the clamped side region and at least a portion of theclamping slot.
 6. The system of claim 5, wherein the spacer has adifferent coefficient of thermal expansion than at least the portion ofthe clamping slot directly adjacent to the spacer.
 7. The system ofclaim 1, including configuring at least one of thetemperature-contractible material, a dimension of the clamping slot, adimension of the clamped side region, and the temperature differentialto achieve a predetermined compressive force between the clamping slotand the clamped side region.
 8. The system of claim 1, wherein asupermajority of a surface area of the clamping slot is in thermalcontact with a supermajority of a surface area of the clamped sideregion to achieve a predetermined rate of thermal energy transfertherebetween.
 9. The system of claim 1, wherein the predeterminedtemperature differential is applied to the clamping slot via at leastone of cooling/heating channels in the card rack, exposure of an entirecircuit card rack system to a desired heating/cooling energy, thermalsiphon, cryogenic liquids, dilution refrigeration, Gifford-McMahon (GM)or pulse tube cryocoolers, and local exposure of at least a portion ofthe clamping slot to a heating/cooling agent.
 10. The system of claim 2,wherein the negative thermal expansion results in the reducedlongitudinal dimension of at least a portion of the clamping slotbringing the clamping slot into compressive contact with the portion ofthe clamped side region which is located longitudinally within theclamping slot, such that the dimensional mismatch between the clampingslot and the clamped side region which is located longitudinally withinthe clamping slot produces the compressive force.